THE ONSET OF FERMENTATIVE METABOLISM IN CONTINUOUS CULTURES DEPENDS ON THE CATABOLITE REPRESSION PROPERTIES OF SACCHAROMYCES-CEREVISIAE

In glucose-limited continuous cultures, a Crabtree positive yeast such as Saccharomyces cerevisiae displays respiratory metabolism at low di lution rates (D) and respirofermentative metabolism at high D. We hypo thesized that the onset of fermentative metabolism is related with the catabolite repression or glucose repression effect. To test this hypo thesis, we have investigated the physiological behavior in glucose-lim ited continuous cultures of S. cerevisiae strain CEN.PK122 and isogeni c mutants, snf1 (cat1 and snf4 (cat3, defective in proteins involved i n the release from glucose repression and the mutant in glucose repres sion mig1. We analyzed the behavior of the wild type and mutant strain s at steady state in chemostat cultures as a function of D. Wild-type cells displayed respiratory metabolism up to a D of 0.2 h(-1). snf1 an d snf4 mutants started fermenting after a D of 0.l and 0.15 h(-1), res pectively. The latter behavior was not due to an impairment of respira tion since their specific rate of oxygen consumption was similar or ev en higher than that shown by the wild type. The snf1 strain displayed much lower yields than the wild type and the other mutants in the whol e range of D studied. We conclude that the onset of fermentative metab olism in yeast growing in chemostat cultures is related with glucose r epression. (C) 1998 Elsevier Science Inc.